1. Field of the Invention
This invention relates to a capacitive-load driving circuit for driving a capacitive load such as the driving circuit of an ink-jet printer head using a piezoelectric element. More particularly, the present invention relates to technology for reducing power consumption as seen from the power supply side in the driving circuit.
The present application is based on Japanese Patent Applications Nos. Hei. 9-277272 and Hei. 10-052197, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In a conventional driving circuit of an ink-jet printer head using a piezoelectric element, ink is sucked and discharged by applying a trapezoidal-wavelike pulse voltage to a piezoelectric element in an ink-jet nozzle to vary the volume of an ink chamber. A push-pull current amplifier circuit using two transistors that are connected together is used in the driving circuit. In the current amplifier circuit, a capacitive load (a piezoelectric element) is charged by a power supply via one transistor, based on the trapezoidal-wavelike pulse voltage (an input signal) that is output from a trapezoidal-wave voltage generating circuit, which is formed at the preceding stage, and the charge is discharged from the capacitive load to ground via the other transistor.
However, the conventional driving circuit has several problems. One problem is high power consumption because the quantity of electricity required to charge the capacitive load is supplied totally from the power supply. Another problem is that a great deal of heat is generated by the transistors because the supply voltage is applied directly across the emitter.sub.-- collector of the transistors when charging of the capacitive load is started. Still another problem is that a great deal of heat is also generated by the transistors because the peak value of the charging voltage is applied directly across the emitter.sub.-- collector of the transistors even when discharging of the capacitive load is started.